1. Field of the Invention
The present invention relates to a paper feeding apparatus of an image forming apparatus, such as an office machine such as a copier, a printer and a fax, and more particularly, to a paper feeding apparatus of an image forming apparatus having an active paper separating unit, which is disposed at a lower part in the paper feeding direction of a stacker or a cassette for stacking paper to rotate in the anti-paper feeding direction and to actively rub leading ends of sheets of paper, thereby separating and feeding the sheets of paper sheet by sheet.
2. Description of the Related Art
An image forming apparatus, such as an office machine, such as a printer and a fax, generally comprises a paper feeding apparatus feeding sheets of paper to an image forming unit.
As shown in FIG. 1, such paper feeding apparatus 10 comprises a frame 11 composing a stacker or a cassette for stacking paper, a pickup unit 30 disposed at the lower side in the paper feeding direction (right hand side of FIG. 1) of the frame 11 to rotate in association with a power transferring gear train (not shown) connected with a pickup roller driving motor (not shown) and to pick up sheets of paper stacked in the frame 11, and a paper separating assembly 40 comprising a plurality of paper separating plates integrally or separately disposed to the frame 11 at the lower side in the paper feeding direction of the frame 11 to separate and feed a sheet of paper at a time while supporting the sheet of paper to enter at a predetermined angle.
The pickup unit 30 comprises a pickup roller assembly 33 comprising a pickup shaft 31 connected to the power transferring gear train, a first gear (not shown) formed around the pickup shaft 31, a first and a second idle gears (not shown) pivotably disposed around a first and a second idle shafts 37, 38 to move in association with the first gear, a pickup roller gear (not shown) connected to the second idle gear, a pickup roller 34 coaxially formed with the pickup roller gear to pick up a sheet of paper, an unidirectional power transfer unit (not shown) such as a spring clutch for transferring rotary power only in the paper pickup direction to the pickup roller gear between the pickup roller gear and the second idle gear, and a link member 36 with one end connected with a pickup roller shaft 39 and the other end pivotably supported on a supporting shaft 35 to support the pickup roller 34 to be in contact with paper.
Hereinafter, the operation of a conventional paper feeding apparatus 10 having the above described structure will be described.
When a paper feed mode is selected, the pickup shaft 31 rotates in the pickup direction, for example, clockwise, by the power transferring gear train connected to the pickup roller driving motor, and accordingly the pickup roller 34 rotates counterclockwise in association with the first gear, the first and second idle gears and the pickup roller gear.
As a result, a sheet of paper in contact with the pickup roller 34 is picked up and fed as the pickup roller 34 rotates counterclockwise.
The paper picked up by the pickup roller 34 is separated sheet by sheet while being supported to be in a predetermined paper-entering angle by the paper separating plates of the paper separating assembly 40 and then conveyed to the image forming unit (not shown).
After that, when the paper activates a paper sensor (not shown), a control unit (not shown) stops the pickup roller driving motor and starts a paper feed roller driving motor (not shown), or transfers the driving force of the pickup roller driving motor to the paper feed roller driving unit (not shown) thereby driving a paper feed roller conveying paper through a power connection/blocking device such as a swing gear (not shown) in order to stop the pickup roller 34 and drive the paper feed roller (not shown).
As a result, the paper is continuously conveyed to the image forming unit by the paper feed roller. The pickup roller 34 receiving counterclockwise rotary force from the paper idle-rotates without transferring rotary force to the pickup roller gear due to the unidirectional power transfer unit of the pickup roller assembly 33.
However, in such conventional paper feeding apparatus 10, a picking up or feeding force of the pickup roller 34 is determined on the basis of a weight of the paper which is commonly used. Accordingly, when sheets of paper which are rarely used are picked up or fed, the paper feeding force is not suitable for such sheets, so that a sheet pickup problem such as a multi sheet feed or a sheet feed failure may occur during paper pickup.
More specifically, currently used papers have various weights ranging from 40 g/m2 to 200 g/m2, but a paper feeding force of the pickup roller 34 is determined on the basis of the paper having a weight ranging from 60 g/m2 to 90 g/m2 which is commonly used. Accordingly, when sheets of paper having a weight of below 60 g/m2 or above 90 g/m2 are picked up, the sheet pickup problem may occur.
To solve such a sheet pickup problem generating when various sheets of paper are fed by one paper feeding force determined as explained as above, the conventional paper feeding apparatus 10 is generally provided with paper separating plates having a paper-entering angle determined to separate and feed sheets of paper sheet by sheet without generating the sheet pickup problem to sheets of paper having a weight of below 60 g/m2 or above 90 g/m2.
However, even though the paper-entering angle of the paper separating plates is determined not to generate the sheet pickup problem to the sheets of paper which are rarely used, if a thickness of and a frictional force between sheets vary as a kind of paper, the paper-entering angle determined like that comes not to tally with that which is required of the sheets to be practically fed by the paper feeding apparatus 10.
Thus, if the paper-entering angle is not tallied (i.e., considered) with the practically required paper-entering angle, the paper feeding apparatus 10 comes to again present the sheet pickup problem such as the multi sheet feed or the sheet feed failure.
To solve this problem, a method of forming the paper separating plates from material having relatively large frictional force such as a rubber, or a method of forming projections on the paper separating plates can be considered. However, these methods have a disadvantage that since the paper separating plates is fixedly disposed, they cannot directly or actively give a frictional force on the sheets, if a paper-entering angle thereof which is required of the sheets to be practically fed does not tally with a paper-entering angle thereof, and thereby there is a limit to what ranges the sheet pickup problem is prevented from occurring.